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Looking for Input from RV-15 Builders On Fuel Tanks

Jetmart

Jetmart

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Sorry for all the questions. Have read a little bit here and there across different threads.

Just wondering what most are doing with pressure testing of the tanks. Testing prior to riveting to rear spar or after?
Has anyone who has tested either standalone tank or after riveting found a leak?
Is there any reason to wait to close up access holes in tanks once the fuel senders are mounted?
Has there been a definitive answer on using the same fuel senders and mounting one upside down from Van's?
Does anyone have an estimate of how much tank sealant is required for access holes and fuel senders?

Getting close to running out of work. Want to move on to tanks but must decide when to order tank sealant. I have 6 year old sealant that has been in the freezer the entire time that I don't plan on using on the tanks.
 
Jetmart said:
Sorry for all the questions. Have read a little bit here and there across different threads.

Just wondering what most are doing with pressure testing of the tanks. Testing prior to riveting to rear spar or after?
Has anyone who has tested either standalone tank or after riveting found a leak?
Is there any reason to wait to close up access holes in tanks once the fuel senders are mounted?
Has there been a definitive answer on using the same fuel senders and mounting one upside down from Van's?
Does anyone have an estimate of how much tank sealant is required for access holes and fuel senders?

Getting close to running out of work. Want to move on to tanks but must decide when to order tank sealant. I have 6 year old sealant that has been in the freezer the entire time that I don't plan on using on the tanks.
Click to expand...

I’m planning to test it prior to installation on the spar.

I have a quart kit of Flamemaster CS 3204 B-2 that vans sent that I’m not using as I prefer the cartridges for my Semco gun.

It is unopened and has an expiration date of 9/26…

Asking $165 shipped CONUS.
 
I would test before installation.

I did not test the left tank on mine, and I fear it may have a leak. I have done the balloon test and gone over every exposed rivet and seam with no bubbles, but the balloon won't hold air and leaks down slowly over 12-24 hours.

I tested the right tank before installation and found no leaks with bubble testing and the balloon (same balloon and test setup) stayed fully inflated for 24+ hours.

I am pondering what to do as there are some rivets and seams that are not really accessible externally once the wing is built. If a leak is identified I am pretty sure almost all areas are accessible from one of the 4 access plates.
 
Jetmart said:
Anyone find a leak? There must be 100 plus kits delivered so far.
Click to expand...
I have not found a leak (at least not LOCATED one), but I think my left tank has one as I mentioned above.

I understand the intent and limitations of the balloon test. I used the same balloon and same equipment on both tanks. On the right tank I went over all seams and rivets, no bubbles. the balloon stayed the same size for >24h.

I have pressurized the left tank 3-4 times now (maybe more) and gone over everything I can access with leak detector fluid. The balloon always steadily deflates to empty over 12-24h. I can't find a leak, but the tank is installed, limiting some access.

If I were starting over I would leak test before installation, which is why I recommended that for people starting the build...
 
I am open to any thoughts on next steps. I’m not exactly sure what I’m going to do yet…
 
TShort said:
I am open to any thoughts on next steps. I’m not exactly sure what I’m going to do yet…
Click to expand...
Repeat the test with a fresh balloon, on the odd chance it developed a leak after the right tank tests but before the left.

Put some 100LL in the tank, stand it up nose high so the spar area is flooded, and wait a couple of days -- see if fuel comes out in a place that would give you some clue about where a leak might be. It would be a shame to drill out all the spar rivets only to find that the leak was elsewhere.
 
You could replace the balloon with a simple water manometer. It would not be prone to leaking like a balloon. As far as balloons go, they are porous and WILL deflate over time, even if they are tied off.
 
I’m virtually certain there is a leak in the tank. I used the same balloon and equipment - first on the L tank about 4-5 times, then moved it to the right tank.
It leaked down every time on the L tank within 12-24 hours. On the R tank, the balloon didn’t change at all over >24h.
Switched it back to the left, and same results x 2.

I went over things again with the leak solution this afternoon. I think there may be a tiny leak at the inboard doubler on the rear spar on the top side. Hard to see in pics but very very faint bubbles:


IMG_7798.jpeg

In the location circled:

IMG_7799.jpeg

There does not seem to be much (any?) proseal on those solid rivets, nor a filet between the two doublers.

I emailed Van’s for thoughts…
 
It is difficult to fix a leak from the outside; could you see that rivet in the inside?

I know you already have the covers installed…
 
If you seal it from the outside first and pull a negative pressure using a hand vacuum pump on the tank for the curing period it will draw sealant in. Then seal the nearby rivets from the inside. Another option is wicking locktite, which is amazing stuff. Also suck it in with a negative pressure. Sometimes takes a few applications but I've sealed crankcase split/sump leaks and intake runners/sump leaks with it several times.
 
Following up on my leak issue above.

I finally broke down and put 5 gallons of avgas in the tank. Within a few minutes I had fuel dripping on the floor.

There is a leak at the bottom aft inboard portion of the tank (hopefully, THE leak - not one of several):


56AEBDE0-EDBC-4078-A2AA-4E9129E3FFEF_1_201_a.jpeg

148E5C88-7EBB-4E90-B267-3042839845FB_1_102_a.jpeg

I did not find it with leak detector initially, as I had to drizzle the fluid down that angled portion of the doubler, and even then the bubbles only lasted a few seconds until the fluid ran off.

Awaiting discussion with Van's, but I will be pulling the inboard inspection plate...
 
I don't think the balloon test is all that reliable. The tanks on our 7 held pressure for days with the balloon inflated. Once filled with fuel, a blue stain appeared within days from both tanks, one was from the vent line fitting where it passes through the rib, the other from a corner pinhole that slowly wicked out fluid during flight. Both required cracking into the tanks after unmounting them. At least the 15 design has the access plates so while it's trouble it isn't downright destructive like having to cut into the back baffle.
 
I used the balloon test to create pressure to use the bubble solution, and only secondarily as a test for a leak.

On the right tank, the balloon stayed inflated for days. Temps in the shop are pretty constant, and I monitored baro pressure.

The left tank deflated within 12-24 hours every time, despite me not initially finding the leak using the leak solution...

That's what prompted the additional testing.
 
I had an RV-12 tank that never leaked on bench testing, but always leaked when installed. The -12 tank is suspended by 3 bolts and the bottom skin leaked with the weight of the fuel above it when suspended, but sealed shut when set upon the bench. Drove me crazy!
 
With the balloon test I find the seal at the balloon being the weak point. You need to seal it tight with tape and a even a zip tie. I tested the first tank with soap and water before I did the wing. Balloon is still inflated after more than a week. If we get a leak behind the spar with fuel, it will be a real challenge to find. Waiting for the other tank to dry to test. I mixed about 30 grams twice and used about 3/4 of it for one tank.

You would have to bend the rod different to make the float miss the nut plate if you use the supplied float on the right tank. I bought the other sender for the right tank as that was just easier and made more sense to me.
IMG_7552.jpeg
 
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